1. Field of the Invention
This invention relates to anionically polymerizable monomers containing at least one silicon or titanium atom, polymers thereof, and use of such polymers in photoresists, particularly for the microelectronics industry. In one aspect this invention also relates to vapour deposition and polymerization of silicon-functionalised cyanoacrylates.
2. Description of the Related Art
The use of anionically (or zwitterionically) polymerisable monomers as resist materials for microlithography is known in the art, as discussed in U.S. Pat. Nos. 4,675,273 Woods et al. and 4,675,270 Woods et. al. both assigned to Loctite (Ireland) Limited, the contents of which are incorporated herein by reference. Such resist materials are usually applied to or formed as a coating on an etchable substrate; the coated substrate is then imaged using high energy radiation; the image is developed by a development process, normally using a solvent; and the image is etched using a suitable plasma or chemical etching process.
Chemical etching has a significant disadvantage in that it is isotropic, i.e. the etching can affect the substrate below the photoresist. To achieve anisotropic etching, it is preferred to use dry etching by radio frequency glow discharge or large area ion beam methods. The most preferred methods are:
(i) plasma etching, e.g. using oxygen or a halocarbon, particularly a fluorocarbon such as CF.sub.4 or CH.sub.2 F.sub.2 with chlorine or argon; or PA1 (ii) reactive ion etching. PA1 (1) coating a substrate with a film that contains a cationic photoinitiator; PA1 (2) exposing the film in an imagewise fashion to radiation and thereby generating cationic initiator in the exposed regions of the film; PA1 (3) treating the exposed film with a cationic sensitive monomer to form a film of polymer resistant to plasma etching; and PA1 (4) developing the resist image by etching with a plasma. PA1 Y is a strong electron withdrawing group containing at least one silicon or titanium atom.
(See "Plasma Etching" by J. A. Mucha and D. W. Hess in "Introduction to Microlithography"(L. F. Thompson, C. G. Willson and M. J. Bowden Ed.) ACS Symposium Series 219, Am. Chem. Soc. (1983), 216-285; and "Multilayer Techniques and Plasma Processing" by A. Reiser in "Photoreactive Polymers--the Science and Technology of Resins", John Wiley & Sons (1989), 359-393).
However in plasma etching the photoresist itself is vulnerable to being etched away. There is a need therefore for polymeric photoresist films which have a good dry etch resistance. It is known to increase the plasma resistance of a resist material by including silicon in it (see the Reiser reference mentioned above, pages 375-381). U.S. Pat. No. 4,551,418 Hult et. al. describes a process for generating a negative tone resist image comprising the steps of:
The cationic sensitive monomer may be an organometallic monomer wherein the organometallic elements include silicon, germanium and tin. Particular examples of monomers include an epoxy substituted siloxane or silane or a silyl substituted vinyl ether. The monomer may be dissolved in a solvent or may be in the vapor state.
However there is no teaching concerning improving the dry etch resistance of anionically polymerizable resist materials.